This invention relates to filters for medical devices and, more particularly, to filters adapted to be placed in or along lines or tubes through which fluids are introduced to or withdrawn from the human body during medical treatment.
Many medical procedures involve the administration of fluids to a patient by injection or infusion. Alternatively, a patient's own body fluids may be withdrawn, subjected to treatment outside the body, and returned to the body following treatment. Examples of such procedures include administration of intravenous (I.V.) solutions, hemodialysis, hemoperfusion, peritoneal dialysis, and blood oxygenation. However, a common incident of such treatments is the iatrogenic introduction of contaminating particles into the patient's body. The risks to patient health posed by these particulate contaminants are a matter of increasing concern among health care providers.
A review of the literature on particle contamination by Marlowe, titled "Particles in Medical Devices," (National Technical Information Service PB81-131625, 1980) reports that "mobile particles from any source subject patients to considerable risk of neurological or vascular damage." The Marlowe review notes that contaminating particles originate in a variety of sources, including glass containers, polyvinyl chloride (PVC) connecting tubing, and injectable fluids such as I.V. solutions. Fibers represent one type of frequently encountered particulate contaminant. It is significant that very small particles, such as those which are capable of passing through a filter with a pore diameter of 2 microns (.mu.m), can cause injury.
One approach to this problem involves the installation of a filter or other screening device in the connecting line between the suspected source of particle contamination and the patient. This approach can be effective. However, in such applications as peritoneal dialysis, in which a fluid is infused into and withdrawn from a body cavity through the same connecting line, a conventional filter is not desirable because it tends to become clogged with cellular and other bodily debris during fluid withdrawal. For example, in peritoneal dialysis, fresh dialysate is infused into a patient's peritoneal cavity where it remains for a time sufficient to permit diffusion and convection of waste materials into the dialysate. After such time, the spent fluid is withdrawn, carrying with it not only the waste materials, but also cellular and other bodily debris from the patient's peritoneal cavity.
Dennehy et al., U.K. Pat. No. 2,063,684, disclose a particle filter on a dialysis line in apparatus for continuous ambulatory peritoneal dialysis (CAPD).
DeVries, U.S. Pat. No. 3,545,438, discloses an apparatus for peritoneal dialysis using unsterilized fresh dialysate. The apparatus includes a filter to remove particles and a second filter to remove bacteria.
In applications such as peritoneal dialysis, the filter can be bypassed during withdrawal by means of a valve-directed shunt. For example, Popovich et al., U.S. Pat. No. 4,239,041, disclose apparatus for continuous ambulatory peritoneal dialysis having a bacterial filter on an inlet line. Between the filter and the entrance to the peritoneal cavity is a valve which can be adjusted to direct fresh dialysate from a reservoir into the peritoneal cavity during infusion, or alternatively, to direct spent dialysate to a collection bag, bypassing the filter.
Valves are undesirable for two reasons. First, valves require that an additional action be undertaken by the operator, frequently a patient. Second, the valve represents an additional inlet or source of bacterial contamination, increasing the risk of patient infection.
Gilpatrick, U.S. Pat. No. 3,930,096, discloses a composite fabric structure which features high resistance to fluid flow in one direction, yet performs a filtration function under conditions of substantially reduced resistance during countercurrent flow. The Gilpatrick device filters fluid flowing in one direction, but substantially checks all flow in the opposing direction.
Muller, U.S. Pat. No. 4,167,482, discloses a filtering apparatus comprising a mop-like filter element relying upon floating or mobile fibers for its effectiveness. Mobile fibrous or filamentous strands are attached to a porous support such that fluid flowing in one direction presses the mobile fibers against the support to form a type of filamentous filter mat. Countercurrent flow mobilizes the strands, freeing them from the mat-like formation, and allows rinsing of the mobilized fibers.
Various one-way valves have been designed which regulate the direction of fluid flow but which do not filter the fluid.